Unit 316 session 2 Unvented systems

​Unvented hot water storage systems

​An unvented hot water storage system is simply a sealed system of pipework and components that is supplied with water above atmospheric pressure. The system does not require the use of a feed cistern. Instead, it is fed with water directly from a water undertaker’s mains supply

Open Ended

What do you think are the benefits if any, of an unvented hot water system?

There are two types of unvented hot water storage cylinders, both are manufactured to BS EN 12897:2006 Specification for indirectly heated unvented (closed) storage water heaters, and available as direct fired/heated or indirectly heated vessels:

​​The types of unvented hot water storage cylinders

Match

Match the following

• Open vented

• Open vented

• Unvented systems

• Unvented systems

• Unvented systems

Storage is available to meet the demands

Space needed for cylider and cistern

Balanced pressures at both hot and cold

Less space required

A high level of maintenance is required

• Storage is available to meet the demands

• Space needed for cylider and cistern

• Balanced pressures at both hot and cold

• Less space required

• A high level of maintenance is required

​unvented hot water storage cylinders incorporating an internal expansion air gap.

unvented hot water storage cylinders using an external expansion vessel

​The direct system uses a direct type unvented hot water cylinder that does not contain any form of heat exchanger.

There are two very different types:

​Direct storage systems

​Electrically heated – this type of cylinder does not contain a heat exchanger.

​Gas or oil fired – the design of these water heaters originated in North America.

They consist of a hot water storage vessel with a flue pipe that passes through the centre.

​Direct unvented under sink storage heaters
Unvented under sink hot water storage heaters are connected direct to the mains cold water supply and deliver hot water at near mains cold water pressure. Because they have less than 15 litres of storage, they are not subject to the stringent regulations that surround the installation of larger unvented hot water storage units.

Drag and Drop

Which of these statements relate to an open vented system?​ ​

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Drag these tiles and drop them in the correct blank above

Storage is available to meet peak demands

Always open to the atmosphere

Water temperature can never exceed 100°C

Balanced pressures at both hot and cold taps

No back up of water

Labelling

Drag the components into their correct places

Drag labels to their correct position on the image

D1 pipework

Pressure relief valve

Temperature relief valve

Expansion vessel

D2 pipework

Labelling

Drag the components into their correct places

Drag labels to their correct position on the image

D2 pipework

Pressure reducing valve

D1 pipework

Check valve

Internal air space

In line strainer

Multiple Choice

What is the main characteristic of an unvented hot water storage system?

• Atmospheric pressure

• Sealed system

• Gravity-fed

• Open components

Multiple Choice

How is water supplied to an unvented hot water storage system?

• Gravity-fed

• Pumped from a feed cistern

• Directly from a mains supply

• Condensed from the atmosphere

Multiple Choice

Why are unvented under sink hot water storage heaters not subject to stringent regulations?

• Limited storage capacity under 15L

• Mains cold water pressure

• External expansion vessel

• Internal expansion air gap